LOS ANGELES, June 4 (Reuters) - California environmental
groups have sued state and federal water managers, claiming that
their drought-management plan for projects below the crucial
Sacramento-San Joaquin River Delta is pushing some species of
fish to the brink of extinction.

The lawsuit marks the latest salvo in the battle over water
in California as the state suffers through its fourth year of a
devastating drought that has prompted strict conservation
measures.

"We bring this lawsuit in an effort to prevent the impending
extinction of fisheries that thrived for millennia," Bill
Jennings of the California Sportfishing Protection Alliance said
in a statement announcing the legal action, which was filed in
U.S. District Court in Sacramento on Wednesday.

"We cannot stand aside and watch species go extinct simply
because special interests have captured our regulatory agencies
and they refuse to comply with laws enacted to protect fish and
water quality," Jennings said.

The lawsuit seeks to block the U.S. Bureau of Reclamation
from enforcing emergency modifications to state and federal
regulations to divert water from fisheries, waterways and
crucial habitats to cities and farmers served by two water
projects below the delta.

A spokeswoman for the Bureau of Reclamation could not
immediately be reached for comment on the lawsuit on Thursday
morning.

Last month California water regulators approved a plan by
some of the state's most senior water rights holders to
voluntarily cut water use by 25 percent in exchange for
assurances that they would not face further curtailments during
the growing season.

Under the first-of-its-kind agreement, so-called riparian
growers in the delta who participate agreed to either reduce
water diversions by 25 percent or fallow one-quarter of their
land.

Riparian land borders natural waterways such as rivers or
streams and the roughly 4,000 growers with such farmland in the
delta hold some of California's priority or most senior, and
typically inalienable, water rights.

That deal comes as California considers curtailing water
diversions to senior water rights holders in the state for the
first time since the late 1970s.

The drought has prompted Governor Jerry Brown to impose the
state's first-ever mandatory cutbacks in urban water use, up to
36 percent in some communities. Brown had been criticized for
largely exempting agriculture from those severe restrictions.

California grows nearly half of all U.S. fruits and
vegetables, mostly in the Central Valley, and ranks as the top
farm state by annual value of agricultural products.
(Reporting by Dan Whitcomb; Editing by Sandra Maler)